Biodegradation Of Hyper-salinity Dye Wastewaters And The Accelerating Effect Of Redox Mediators

The purpose of this dissertation is to acclimate and isolate the salt-tolerant bacteria and investigate the accelerating effect of redox mediators in the bio-decolorization, which is used to solve the two possible bottlenecks of anaerobic-aerobic biotreatment of azo dyes: (1) high salinity of the dye wastewaters usually causes plasmolysis and/or loss of activity of cells, and some traditional aerobic- and anaerobic-biological treatments in low BOD removal performance;(2) anaerobic azo dye reduction is a time-consuming process, reflected by the requirement of long reaction times.Firstly, Three salt-tolerant mixed cultures (AS, SW, TAS) were acclimatized by the gradually increasing NaCl concentration and these acclimatized cultures could decolorize the 13 selected dyes with high salt concentration. The effects of salt concentration and dye concentration on decolorization rate were compared. With the elevated concentrations of salt and dye, the decolorization was lower. The abilities of decolorization by three mixed cultures were studied.Secondly, Degradation and inhibition kinetics of Reactive Brilliant Red K-2BP by salt-tolerant mixed culture were developed based on experimental results at different salt (NaCl) concentrations (5-150 g L^-1) and different dye concentrations (100-600 mg L^-1). The observed kinetic reaction coefficient was determined and correlated as a function of salt and dye concentration. The degradation rate follows first order kinetics with respect to dye concentration. Salt inhibition was expressed as a hyperbolic function. The values of K_T and K_IS were 39.784±27.169 g L^-1 and 329.524±175.822 mg L^-1, respectively.Then, The accelerating effect of redox mediators in the bio-decolorization was conducted. Decolorization of azo dyes was carried out experimentally using the salt-tolerant bacteria under redox mediators and high salt conditions. Anthnaquinone and bromoamine acid used as redox mediators were able to increase the decolorization rate of wastewater containing azo dyes. High decolorization rate was obtained in the presence of redox mediators at 30℃, which increased 1.5-5 fold, in comparison with the control of redox mediators. The experiments explored a great improvement of the redox mediator application and the new bio-treatment concept.Experiments were also conducted to study some electrochemical factors affecting the bacterial reduction (cleavage) of four azo dyes. And a common mixed culture was used as test organism and the reduction of azo dyes Acid Yellow 4, 11, 17 and Acid Yellow Bis was studied. It was found that the azo dyes were reduced at different rates, which could be correlated with the reduction potential of the azo compounds in cyclic voltammetric experiments. Acid Yellow bis (Er -616.75 mV) was reduced at the highest rate of 0.01209 mol (g cell protein)'1 (h)"1, Acid Yellow 11 (Er -593.25 mV) at 0.01040 mol (g cell protein)'1 (h)"1 and Acid Yellow 4 (Er -513 mV) at 0.007575 mol (g cell protein)"1 (h)"1. It was showed that the reduction potential would be a preliminary tool to predict the decolorization capacity of oxidative and reductive biocatalysts.Meanwhile, this work was conducted to study the change characteristics of the oxidation-reduction potentials (ORP) during the process of the biological decolorization of azo dyes, knowledge of which will be useful in the prediction of the decolorization capacity of oxidative and reductive biocatalysts. Reduction of these azo dyes did not occur under aeration conditions, and azo dyes were reduced by microorganisms only when the Oxidation-Reduction Potential (ORP) values decrease the certain limits (<-93 mV) during the decolrization processes. At the same time, sulfate salt, anthnaquinone (AQ) and 1-amino -4-bromo-2-anthraquinonesulfonic acid (BAA) were tested to assess the effects on the change of ORP during the decolorization process. These studies with the salt-tolerant mixed culture indicate that the reduction of azo dyes might be influenced by the chemical nature of the azo compound and redox mediatorsAt last, strain GTW and GTY were isolated and identified as Halomonas sp. and Gracilibacillus sp. based on morphological and physio-biochemical characteristics and 16S rDNA sequence analysis, and were deposited as patent strains in China General Microorganism Culture Center with the accession number CGMCC 1528 and CGMCC 1527, respectively. The 16S rDNA sequence of strain strain GTW and GTY were also submitted to GenBank with the number DQ 279849 and DQ 286727, respectively.